Internal axial light conduction in the stems and roots of herbaceous plants

In order to reveal any roles played by stems and roots of herbaceous plants in responding to the surrounding light environment, the optical properties of the stem and root tissues of 18 herbaceous species were investigated. It was found that light was able to penetrate through to the interior of the stem and was then conducted towards the roots. Light conduction was carried out within the internodes and across the nodes of the stem, and then in the roots from the tap root to lateral roots. Light conduction in both the stem and root occurred in the vascular tissue, usually with fibres and vessels serving as the most efficient axial light conductors. The pith and cortex in many cases were also involved in axial light conduction. Investigation of the spectral properties of the conducted light made it clear that only the spectral region between 710 nm and 940 nm (i.e. far-red and near infra-red light) was the most efficiently conducted in both the stem and the root. It was also found that there were light gradients in the axial direction of the stem or root, and the light intensity generally exhibited a linear attenuation in accord with the distance of conduction. These results revealed that tissues of the stem and root are bathed in an internal light environment enriched in far-red light, which may be involved in phytochrome-mediated metabolic activities. Thus, it appears that light signals from above-ground directly contribute to the regulation of the growth and development of underground roots via an internal light-conducting system from the stem to the roots.     

Stem anatomy of Dolichos lablab Linn (Fabaceae): Origin of cambium and reverse orientation of vascular bundles

Secondary growth in the stem of Dolichos lablab is achieved by the formation of eccentric successive rings of vascular bundles. The stem is composed of parenchymatous ground tissue and xylem and phloem confined to portions of small cambial segments. However, development of new cambial segments can be observed from the obliterating ray parenchyma, the outermost phloem parenchyma and the secondary cortical parenchyma. Initially cambium develops as small segments, which latter become joined to form a complete cylinder of vascular cambium. Each cambial ring is functionally divided into two distinct regions. The one segment of cambium produces thick-walled lignified xylem derivatives in centripetal direction and phloem elements centrifugally. The other segment produces only thin-walled parenchyma on both xylem and phloem side. In mature stems, some of the axial parenchyma embedded deep inside the xylem acquires meristematic activity and leads to the formation of thick-walled xylem derivatives centrifugally and phloem elements centripetally. The secondary xylem comprises vessel elements, tracheids, fibres and axial parenchyma. Rays are uni-multiseriate in the region of cambium that produces xylem and phloem derivatives, while in some of the regions of cambium large multiseriate, compound, aggregate and polycentric rays can be noticed.     

Successive cambia in Aizoaceae: products and process

The transverse and longitudinal sections of the stems and roots of 11 genera of Aizoaceae, representing a wide range of growth forms from hard fibrous stems to fibre‐free roots, were studied using light microscopy and scanning electron microscopy. In most of the genera, fibres are the first xylary product of each vascular cambium, followed by vessels in a parenchyma background. Variations on this pattern help to prove that fibres are produced by vascular cambia, except in Ruschia and Stayneria, in which both the lateral meristem and the vascular cambia produce fibres. Cylinders of conjunctive tissue parenchyma that alternate with the vascular cylinders are produced by the lateral meristem. The concept that the lateral meristem gives rise to the vascular cambia and secondary cortex is supported by photographic evidence. Radial divisions occur in the origin of the lateral meristem, and then again as vascular cambia arise from the lateral meristem; these radial divisions account for storeying in fibres and conjunctive tissue. Raylessness characterizes all Aizoaceae studied, with the exception of Tetragonia, which also differs from the remaining genera by having vasicentric axial parenchyma, a scattering of vessels amongst fibres, and the presence of druses instead of raphides. Several vascular cambia are typically formed per year. Several vascular cambia are active simultaneously in a given stem or root. Roots have fewer fibres and more abundant conjunctive tissue parenchyma than stems. Successive cambia result in an ideal dispersion of vascular tissue with respect to water and photosynthate storage and retrieval capabilities of the parenchyma, and to liana stem plans. The distribution and relative abundance of fibres, vessels, secondary phloem, and conjunctive tissue parenchyma relate primarily to habit and are not a good source of systematic data, with the probable exception of Tetragonia. The general pattern of lateral meristem and vascular cambial ontogeny is the same as in other families of the core Caryophyllales, although the patterns of the tissues produced are diverse. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 141–155.     

波温苏铁(Bowenia spectabilis)营养器官的解剖结构研究

报道了波温苏铁Bowenia spectabilis Hook.ex Hook. f）根、茎、叶的解剖结构.根的初生结构由表皮、皮层和中柱三部分组成,为二原型木质部.茎具大量薄壁组织,薄壁细胞富含淀粉粒,维管束为外韧并生.叶柄中含有5-8束维管束,呈弧形排列.羽片叶角质层厚,有小叶脉产生,气孔主要分布在下表皮.根、茎、叶木质部中的管胞主要是螺纹和孔纹管胞,有少量纤维分化;茎中管胞的侧壁呈现凹凸不平,部分管胞具有分枝或分叉现象.     

The Application of the Modified Sine Rule to Tension Wood Production and Eccentric Growth in the Stem of Crack Willow (Salix fragilis L.)

One-year-old shoots of S. fragilis were placed on speciallyprepared frames and grown at various angles from the uprightposition for six-and-a-half months. At the end of this periodthe stems were found to have made greater growth on the upperside than the lower, and the majority of the fibres of the upperxylem were of the gelatinous type. The degree of eccentricityand the amount of gelatinous fibres produced were clearly shownto reach a maximum when the stems were displaced by 120°from the upright position. This provides evidence that in stems,as in roots, geotropic responses are not proportional to thesine of the angular displacement from the vertical, but followa modified sine relationship. These results are considered toprovide support for the hypothesis that statolith graviperceptorsmust be present close to the vascular cambium along the lengthof young woody stems. There is no reason to suppose that theperception of gravitational stimulus in stems is in any materialway different from that in roots.     

Xylem of early angiosperms: Novel microstructure in stem tracheids of Barclaya (Nymphaeaceae)

Pit membranes of stem tracheids of all recognized species of Barclaya, an Indomalaysian genus of Nymphaeaceae, were studied with scanning electron microscopy (SEM). Pit membranes of the tracheids are composed of two thick layers, both constructed of fibrils much larger than those of tracheary elements of angiosperms other than Nymphaeaceae. The outer (distal) layer, which comprises the continuous primary wall around the tracheids, is spongiform, perforated by porosities of relatively uniform size, and confined to or most prominent on end walls of stem tracheids. The second layer consists of thick widely spaced fibrils that are oriented axially and are laid down proximally (facing the cell lumen) to the first (outer) layer, although continuous with it. These axial fibrils are attached at their ends to the pit cavities. This peculiar microstructure is not known outside Nymphaeaceae except in Brasenia and Cabomba (Cabombaceae, Nymphaeales), and has not been previously described for Barclaya. The longitudinally oriented threads and strands in perforation plates of secondary xylem of wood and stems of a variety of primitive woody angiosperms (e.g., Illicium) are not homologous to the pit membrane structure observed in stem tracheids of Barclaya, which, like other Nymphaeaceae, has only primary xylem and no perforation plates. The tracheid microstructure reported here is different from pit structures observed in any other group of vascular plants, living or fossil. The tracheid stem microstructures of Barclaya and other Nymphaeaceae appear to be a synapomorphy of Nymphaeaceae and Cabombaceae, and need further study with respect to ultrastructure and function.     

Observations on the vegetative anatomy of Austrobaileya: habital, organographic and phylogenetic conclusions

For the single species of Austmbaileya (Austrobaileyaceae), quantitative and qualitative data are offered on the basis of a mature stem and a root of moderate diameter. Data available hitherto have been based on stems of small to moderate diameter, and roots have not previously been studied. Scanning electron microscope (SEM) photographs are utilized for roots, and show compound starch grains. Roots lack sclerenchyma but have relatively narrow vessels and abundant ray tissue. Recent phylogenies group Austrobaileyaceae with the woody families Illiciaceae, Schisandraceae, and Trimeniaceae (these four may be considered Illiciales), and somewhat less closely with the vesselless families Amborellaceae and Winteraceae and the aquatic families Cambombaceae and Nymphaeaceae. The vessel-bearing woody families above share vessels with scalariform perforation plates; bordered bars on plates; pit membrane remnants present in perforations; lateral wall pitting of vessels mostly alternate and opposite; tracheids and/or septate fibre-tracheids present; axial parenchyma vasicentric (sometimes abaxial); rays Heterogeneous Type I; ethereal oil cells present; stomata paracytic or variants of paracytic. Although comparisons between vessel-bearing and vesselless families must depend on fewer features, Amborellaceae and Winteraceae have no features incompatible with their inclusion in an expanded Illiciales.     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

The anatomy of the chi-chi of <Emphasis Type="Italic">Ginkgo biloba</Emphasis> suggests a mode of elongation growth that is an alternative to growth driven by an apical meristem

The chi-chi of Ginkgo biloba L. are cylindrical woody structures that grow downwards from the branches and trunks of old trees, eventually entering the soil where they give rise to adventitious shoots and roots. Examination of segments of young chi-chi taken from a mature ginkgo tree revealed an internal woody portion with irregular growth rings of tracheid-containing secondary xylem covered by a vascular cambium and bark. The cambium was composed of both fusiform cells and parenchymatous ray cells. Near the tip of the chi-chi, these two types of cambial cells had orientations ranging between axial, radial and circumferential with respect to the cylindrical form of the chi-chi. The xylem rays and tracheids that derived from the cambium showed correspondingly variable orientations. Towards the base of the chi-chi, the fusiform cells and young tracheids were aligned parallel to the axis, indicating that the orientation of the cambial cells in basal regions of the chi-chi gradually became normalised as the tip of the chi-chi extended forwards. Nevertheless, in such basal sites, tracheids near the centre of the chi-chi showed variable orientations in accordance with their mode of formation during the early stages of chi-chi development. The initiation of a chi-chi is proposed to derive from a localised hyperactivity of vascular cambial-cell production in the supporting stem. The chi-chi elongates by tip growth, but it does so in a manner different from organ growth driven by an apical meristem. It is suggested that the chi-chi of Ginkgo is an “evolutionary experiment” that makes use of the vascular cambium, not only for its widening growth but also for its elongation.     

Stem and wood allometric relationships in Cacteae (Cactaceae)

Allometric relationships in organisms are considered a universal phenomenon. A positive scaling has been reported between stem size and cellular size of tracheary elements in wood of different vascular plants, but few studies have been carried out in slow-growing succulent plants. The aim of this study was to evaluate if a relationship exists between size, growth form and wood cell size among individual species of Cacteae. Forty-four species belonging to 16 genera of the tribe Cacteae with differing growth forms and sizes were studied. When analyzing plant size, we found a positive allometric scaling and the larger-sized species showing a higher percentage of succulent tissue and less accumulation of wood tissue. The positive scaling found between plant size (height and diameter) and vessel elements and fiber length support the universality of the allometric relationship proposed for other vascular plants with non-succulent stems. Notably, wide-band tracheids do not scale with plant size or growth form. Succulence associated with narrow vessel elements with distinctive helical secondary walls and wide-band tracheids suggest they are the key adaptations to tolerate drought and provide support to the stems of most taxa in Cacteae. Fibers do not have the primary role of giving mechanical support; therefore, we assume the scarce fibers in clusters represent reaction wood that, along with the fundamental tissue, maintains the vertical position and shape of those species growing in rocky cracks. Our results with species having short succulent stems support the universal theory of positive allometric scaling of vascular plants.     

Scaling of respiration to nitrogen in leaves, stems and roots of higher land plants

Using a database of 2510 measurements from 287 species, we assessed whether general relationships exist between mass-based dark respiration rate and nitrogen concentration for stems and roots, and if they do, whether they are similar to those for leaves. The results demonstrate strong respiration–nitrogen scaling relationships for all observations and for data averaged by species; for roots, stems and leaves examined separately; and for life-forms (woody, herbaceous plants) and phylogenetic groups (angiosperms, gymnosperms) considered separately. No consistent differences in the slopes of these log–log scaling relations were observed among organs or among plant groups, but respiration rates at any common nitrogen concentration were consistently lower on average in leaves than in stems or roots, indicating that organ-specific relationships should be used in models that simulate respiration based on tissue nitrogen concentrations. The results demonstrate both common and divergent aspects of tissue-level respiration–nitrogen scaling for leaves, stems and roots across higher land plants, which are important in their own right and for their utility in modelling carbon fluxes at local to global scales.     

Expression of the Fusarium resistance gene I-2 colocalizes with the site of fungal containment

The tomato resistance gene I-2 is one of at least six members of a gene family that are expressed at low levels in the roots, stems and leaves of young tomato plants. Plants transformed with constructs containing a functional I-2 promoter fused to the beta-glucuronidase (GUS) reporter gene were used in detailed expression studies. Highest GUS activity was found in stems of young tomato plants. Histochemical analysis revealed that the I-2 promoter drives expression of the reporter gene in vascular tissue of fruits, leaves, stems and mature roots. In younger roots, expression was most abundant at the base of lateral root primordia. Microscopical analysis of young tomato plants revealed expression in tissue surrounding the xylem vessels. We show that in resistant plants, fungal growth into this region of the vascular tissue is prevented, suggesting a correlation with the I-2-mediated resistance response.     

Stem anatomy of the dwarf subshrub Cressa cretica L. (Convolvulaceae)

Stem anatomy and development of medullary phloem are studied in the dwarf subshrub Cressa cretica L. (Convolvulaceae). The family Convolvulaceae is dominated by vines or woody climbers, which are characterized by the presence of successive cambia, medullary- and included phloem, internal cambium and presence of fibriform vessels. The main stems of the not winding C. cretica shows presence of medullary (internal) phloem, internal cambium and fibriform vessels, whereas successive cambia and included phloem are lacking. However, presence of fibriform vessels is an unique feature which so far has been reported only in climbing members of the family. Medullary phloem develops from peri-medullary cells after the initiation of secondary growth and completely occupies the pith region in fully grown mature plants. In young stems, the cortex is wide and formed of radial files of tightly packed small and large cells without intercellular air spaces. In thick stems, cortical cells become compressed due to the pressure developed by the radial expansion of secondary xylem, a feature actually common to halophytes. The stem diameter increases by the activity of a single ring of vascular cambium. The secondary xylem is composed of vessels (both wide and fibriform), fibres, axial parenchyma cells and uni-seriate rays. The secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. In consequence, Cressa shares anatomical characteristics of both climbing and non-climbing members. The structure of the secondary xylem is correlated with the habit and comparable with that of other climbing members of Convolvulaceae.     

On Arborescence in Gahnia clarkei and Gahnia sieberiana

Specimens of Gahnia sieberiana from Brisbane, Queensland, andof Gahnia clarkei from near Orbost, Victoria, were collectedand examined both morphologically and anatomically. The speciesgrow in wet areas and are of interest because they representthe largest arborescent species known in the Cyperaceae. Stemdiameters up to 120 mm and stems up to 10 m long have been observed.Such long stems tend to be supported by nearby vegetation. Althoughfresh stems are tough and woody, they are brittle. Branchingof the stems is sympodial, and numerous branches are producedby plants growing in exposed habitats. There is less branchingin plants from shaded habitats. Basal shoots may also occur.Adventitious roots develop basally on most plants, but withG. sieberiana, some adventitious roots form near the shoot apexand grow in and around leaf bases. Anatomical features of interestare an endodermoid layer composed of sclereids with elongate,undulated, outer tangential walls that are lignified and suberized,short vessel elements with horizontal to oblique simple perforationplates, and relatively short sclereids surrounding vessel elementsin the vascular bundles. Some vascular bundles are bipolar.The presence of short vessel elements here is in marked contrastto the longer tracheary elements in other arborescent monocotyledons. Arborescence, stem anatomy, Cyperaceae, Gahnia, saw sedge, Monocotyledon, bipolar bundles, morphology, endodermoid layer     

Carbohydrate partitioning and metabolism during acclimatization of micropropagated Calathea

Regulation of carbohydrate metabolism and compartmentation were studied during the acclimatization of tissue cultured Calathea plantlets. At transplantation plants were characterised by a heterotrophic metabolism with roots and stems as the main storage organs for carbohydrates. As acclimatization proceeded, a switch to autotrophic growth was observed: leaves became source organs, which was among others reflected by significant increases of invertase, sucrose synthase and sucrose-P synthase activities. Mobilization of reserves in roots and stems was also observed during the same period. Sucrose and starch accumulation in leaves was positively correlated with increasing light intensity.     

两种麻黄根与茎次生木质部的解剖与进化和干旱环境的关系

用光镜及扫描电镜对两种麻黄根、茎次生木质部进行了解剖研究,结果表明：轴向系统主要由导管和管胞组成。横向系统由细胞壁木质化了的射线薄壁组织细胞组成。导管直径甚小,多孔式穿孔板,并存在导管与管胞之间的管状分子类型,推断麻黄属是裸子植物中最早出现导管的类群;管胞中有一些两头尖、胞腔小、具缘纹孔含纹孔塞的长分子,可视作纤维状管胞,使管胞的输导作用被削弱,而支持功能被加强;射线异型多列,已不具备裸子植物具较窄射线的特点。导管与管胞并存,恰好起到了一般沙生被子植物具宽窄两种类型的导管、复孔率高等典型的对干旱环境的适应特征的作用,茎中导管分子的长度和宽度均小于根,这与茎部需要较强的机械支持力相一致。     

Carbon isotopic composition of legumes with photosynthetic stems from mediterranean and desert habitats

The carbon isotopic compositions of leaves and stems of woody legumes growing in coastal mediterranean and inland desert sites in California were compared. The overall goal was to determine what factors were most associated with the carbon isotope composition of photosynthetic stems in these habitats. The carbon isotope signature (d13C) of photosynthetic stems was less negative than that of leaves on the same plants by an average of 1.51 ± 0.42 ;pp. The d13C of bark (cortical chlorenchyma and epidermis) was more negative than that of wood (vascular tissue and pith) from the same plant for all species studied on all dates. Desert woody legumes had a higher d13C (less negative) and a lower intercellular CO2 concentration (Ci ) (for both photosynthetic tissues) than that of woody legumes from mediterranean climate sites. Differences in the d13C of stems among sites could be entirely accounted for by differences among site air temperatures. Thus, the d13C composition of stems did not indicate a difference in whole-plant integrated water use efficiency (WUE) among sites. In contrast, stems on all plants had a lower stem Ci and a higher d13C than leaves on the same plant, indicating that photosynthetic stems improve long-term, whole-plant water use efficiency in a diversity of species.     

The Measurement and Interpretation of Ultrasound from Woody Stems

A system for detecting and counting ultrasonic acoustic emissions(AEs) from woody stems in the waveband of 0.1–1.0 MHzis described. AEs from small pieces of stems of Mains sylvestrisand Chamaecyparis lawsoniana occurred up to a rate of 6000 min^–1,and could be related to the water loss as the stems dried. AEsdid not occur randomly, but were aggregated. Each event is interpretedas a single cavitation occurring in the water within a tracheidor fibre. AEs could be temporarily stopped by rewetting thetissue or cutting it to release tension. From knowledge of thenumber of cells in the stems, the fraction of total counts pernumber of tracheids or fibres present in the stem was calculated.This was found to be less than 0.16. One reason why this fractionis so low is that AEs may occur simultaneously; it is also probablethat some AEs emit energy outside the waveband studied. Eventhough the fraction of AEs recorded is low, this instrumentcould prove to be a very powerful tool for investigating theoccurrence of cavitation in woody stems. Key words: Ultrasound, Cavitation, Wood